Abstract There is growing interest in N 2 O and CH 4 transport through rice plants, but very little information is available on the effects of inhibitors on these gaseous emissions during rice growth and through rice plants. The closed chamber technique was used to study the ef- fect of the urease inhibitor hydroquinone (HQ) and the nitrification inhibitor dicyandiamide (DCD) on N 2 O and CH 4 emissions. As rice plants grew, the N 2 O emission through rice plants was significantly reduced in all treat- ments; N 2 O emissions were always lower in the presence than in the absence of inhibitor(s). These variations par- alleled those in NO 3 – -N content of fresh rice plants. Dur- ing the rice growth period, increasing NO 3 – -N content in rice plants paralleled the increase in the N 2 O emission through rice plants. Hence, NO 3 – -N in young rice plants can substantially contribute to the plant-mediated N 2 O flux. A substantial CH 4 emission through rice plants oc- curred at their vigorous growth stage; CH 4 emissions were always lower in the presence than in the absence of inhibitor(s). Under the experimental conditions, applica- tion of DCD, especially of DCD+HQ, could significantly improve the growth of rice, and reduce the emissions of N 2 O and CH 4 during rice growth. Keywords Dicyandiamide · Hydroquinone · Methane · Nitrous oxide · Urea Introduction Rice fields have been considered as one of the important sources of atmospheric CH 4 (Khalil and Rasmussen 1983; Bartlett and Harriss 1993). For permanently flood- ed rice fields, >80% of CH 4 is emitted from rice plants (Nouchi et al. 1990). The pattern and amount of aeren- chyma in rice plants can substantially contribute to the wide variation in the CH 4 transport capacity of rice plants during different growth stages (Aulakh et al. 2000; Wassmann and Aulakh 2000). Khalil et al. (1998) showed a large N 2 O emission from rice fields using N-based fertilizers. By comparing N 2 O emissions in chambers with and without rice plants, Mosier et al. (1990) showed that young rice plants facilitated the emission of N 2 O. In recent years there has been growing interest in N 2 O and CH 4 emissions through rice plants (Yu et al. 1997; Yan et al. 2000). When soils were flood- ed, N 2 O emissions through rice plants were substantial. The reduction of NO 3 – -N in fresh plants can influence N 2 O and NO x fluxes within the plants and contribute to total N 2 O through the plants (Chen et al. 1990; Klepper 1990; Rockel et al. 1996). Under flooded conditions, dicyandiamide (DCD), a nitrification inhibitor, alone or in combination with hy- droquinone (HQ), a urease inhibitor, can substantially re- duce CH 4 emission during rice growth (Xu et al. 2000a) and effectively regulate the behaviour of applied urea (U)-N in a soil-plant system (Xu et al. 2000b, 2001). This could possibly affect the N loss as N 2 O from rice fields after application of U, and the status of N in the rice plants. Majumdar et al. (2000) and Kumar et al. (2000) showed that in field experiments, application of DCD to- gether with U significantly reduced N 2 O emission. In the presence of nitrification inhibitors such as DCD (Lindau et al. 1993; Xu et al. 2000a), wax-coated CaC 2 (Lindau et al. 1993; Keerthisinghe et al. 1993) and nitrapyrin (Keerthisinghe et al. 1993) and Nimin (Rath et al. 1999), CH 4 emission was significantly reduced from rice fields fertilized with U. Even so, very little information is X. Xu ( ✉ ) · Y. Wang · Y. Huang · X. Zheng · F. Hu State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, People’s Republic of China e-mail: xingkai_xu@hotmail.com Tel.: +86-10-82084278, Fax: +86-10-62041393 P. Boeckx · O. Van Cleemput Laboratory of Applied Physical Chemistry, Faculty of Agricultural and Applied Biological Sciences, University of Ghent, 9000, Gent, Belgium Biol Fertil Soils (2002) 36:53–58 DOI 10.1007/s00374-002-0503-3 ORIGINAL PAPER X. Xu · P. Boeckx · Y. Wang · Y. Huang · X. Zheng F. Hu · O. Van Cleemput Nitrous oxide and methane emissions during rice growth and through rice plants: effect of dicyandiamide and hydroquinone Received: 18 July 2001 / Accepted: 25 March 2002 / Published online: 19 July 2002 © Springer-Verlag 2002